1. Field of the Invention
This invention relates to a method and an apparatus for receiving synchronizing signals from a device for controlling a television camera and converting the received synchronizing signals into a new synchronizing signal.
2. Description of the Prior Art
In a monitor television system used, as one of information transmission systems, at least one television monitor is connected through an electronic switch to a plurality of television cameras and a plurality of transmission lines. The electronic switch provides selection of any one of the television cameras or sequential switching and displaying on the television monitor a picture image of one camera after another.
In such an information transmission system, it is necessary to mutually lock the internal synchronizing signals of a plurality of television cameras to an external synchronizing signal, in order
As one of the devices for synchronizing a plurality of television cameras, there is known an apparatus for transmitting a horizontal synchronizing signal and a vertical synchronizing signal used in a television system, from an external synchronizing generator to the television cameras, and driving the television camera by the transmitted horizontal synchronizing signal, and the vertical synchronizing signal, or the composite synchronizing signal.
Another known apparatus for synchronizing a plurality of television cameras, is an apparatus for transmitting an external synchronizing signal from an external synchronizing generator to the television cameras and locking an internal synchronizing signal generator of the television camera by means of the transmitted external synchronizing signal. Such an apparatus is disclosed in U.S. Pat. No. 4,603,352, the contents of which are incorporated herein by reference.
In any of the above known devices of the type under discussion, as the transmitted synchronizing signal itself is a train of pulses, which can be easily influenced by noise, the transmission of a synchronizing signal requires the use of a coaxial cable with its high shielding effect, which makes it difficult to transmit the synchronizing signal over long distance.
Another apparatus for synchronizing plurality of television cameras is an apparatus for generating two or more frequency signals having frequencies higher than that of the synchronizing signal and different from each other and alternately transmitting the two or more frequency signals to the terminal equipment via low cost twisted pair wires.
The television camera, receives the two or more frequency signals transmitted from the external synchronizing signal generator, decodes the signal in accordance with the alternating rate of the received two or more frequency signals, and synchronizes the camera's internal sync generator on the basis of the decoded signal.
Such an apparatus is disclosed in U.S. patent application Ser. No. 788,987 filed Nov. 7, 1991.
Since the above mentioned synchronizing signals are different, the synchronizing signals transmission methods are different, the apparatuses of this kind are respectively constructed different systems, depending on the synchronizing signals to be used, and are available in markets. Therefore, the instruments to be used are not interchangeable.